Cell cycle-dependent localization of two novel prokaryotic chromosome segregation and condensation proteins in Bacillus subtilis that interact with SMC protein

Disruption of ypuG and ypuH open reading frames in Bacillus subtilis leads to temperature-sensitive slow growth, a defect in chromosome structure and formation of anucleate cells. The genes, which were named scpA and sepB, were found to be epistatic to the smc gene. Fusions of ScpA and ScpB to the fluorescent proteins YFP or CFP showed that both proteins colocalize to two or four discrete foci that were present at mid-cell in young cells, and within both cell halves, generally adjacent to chromosomal origin regions, in older cells. ScpA and ScpB foci are associated with DNA and depend on the presence of SMC and both Seps. ScpA and ScpB are associated with each other and with SMC in vivo, as determined using the FRET technique and immunoprecipitation assays. Genes similar to scpA and scpB are present in many bacteria and archaea, which suggests that their gene products form a condensation complex with SMC in most prokaryotes. The observed foci could constitute condensation factories that pull DNA away from mid-cell into both cell halves.